1. Field of the Invention
The present invention relates to a compound diagnostic X-ray system made by combining an X-ray fluoroscopy apparatus with an X-ray CT scanner. More particularly, this invention is concerned with a diagnostic X-ray system enabling use of information of slice positions in common between the X-ray CT fluoroscopy apparatus and the X-ray CT scanner in a manner that the slice positions are determined using a computed-radiography (CR) image produced from the X-ray fluoroscopy apparatus.
2. Description of the Related Art
In general, for producing tomographic images of a diagnostic region of a patient body using an X-ray CT scanner, it is necessary to determine slice positions accurately. For determining slice positions, the X-ray CT scanner produces an X-ray fluoroscopic image referred to as a scanogram. The slice positions are determined by a physician or the like (operator) while the scanogram is being viewed.
For example, in the case of a rotate-rotate CT scanner, an X-ray tube and detectors are not rotated but held stationary, and X-rays are irradiated while a patient (couch) is being moved unidirectionally (for example, one direction along a body-axis direction of a patient) at a comparatively slower constant speed. In this case, as shown in FIG. 1A, a scanogram analogous to an ordinary X-ray fluoroscopic image is produced. A physician or the like determines slice positions (in FIG. 1A, for example, slice position A of a slice containing a lesion). In the X-ray CT scanner, an X-ray scan is performed at the determined slice positions, thus tomographic images are provided, as shown in FIG. 1B, for example.
However, the scanogram is, as mentioned above, produced by irradiating X-rays while the patient couch is being moved for a certain interval. A scan time gets longer by the time required for moving the patient couch. In other words, the scanogram is not an instantaneously-produced image unlike an X-ray fluoroscopic image. There is therefore difficulty in accurately imaging a region that makes a quick motion (for example, a vessel). It is sometimes hard to determine slice positions accurately.
Moreover, needed as a patient X-ray dose is at least an exposure dose obtained by irradiating X-rays for the period of time required for moving the patient couch. From the viewpoint of minimizing an X-ray dose, desirably, an X-ray fluoroscopic image of a patient should be produced with instantaneous exposure alone.
In almost all cases, the scanogram produced by an X-ray CT scanner is inferior to a fluoroscopic image (CR image), which is a digitized image produced by an X-ray TV unit or the like including, for example, a two-dimensional detector such as an image intensifier (I.I.) and a TV camera, in terms of contrast and resolution. It is therefore hard to locate a lesion using the scanogram. This results in an increase in time required for determining slice positions, and brings about not only the fear of lacking precision in determining slice positions but also remarkably increased time for the scan planning which will lower the patient throughput.